The present invention pertains to a drive for screening machines which sort objects. Specifically, the present invention relates to a drive for use in a machine, known as a mass particle screening machine, for separating material based on particle size. The screening machine is essentially a box having trays of sloping screen plates with varying size mesh openings. A drive having a rotating eccentric weight gyrates the screening box, thus causing the particles to pass through one screen to another screen sorting the particles by specific size.
Examples of known drive units for chip screening machines include U.S. Pat. No. 4,308,758, issued to Humphrey, which discloses a drive box having a fixed shaft and a single rotating eccentric weight fixed to a rotating bearing assembly.
Another drive unit manufactured by KONE WOOD of Salpakangas, Finland, has split weight on a rotating shaft. The split weights of the KONE WOOD invention are located above and below the chip screening machine and are connected by a shaft which passes through the screens of the machine. This shaft arrangement in the KONE WOOD machine impedes and obstructs the horizontal flow of wood chips on the various screens.
A drive unit manufactured by Forano teaches a single weight connected directly to a rotating shaft. The Forano drive unit requires precise machining of the shaft and bearing assembly due to the fact that it employs a single weight rotating with the shaft. Specifically, the bearing housings must be machined concentrically, the bearings must be precisely aligned, and the shaft must be plumb. Unlike the present invention, screening machines with these types of drives often suffer structural failure by operation at high levels of weight revolution 200 RPM or more) if the drives are not manufactured properly.
A drive unit manufactured by CAE Machinery, Ltd., teaches a single weight connected directly to an upstanding and rotating shaft allowing the weight controid to be colinear with the shaft, bearing, and screening machine centroid of mass. The bearing housing hub flange is bolted onto a base plate and the shaft is extended or cantilevered out of the housing. This drive may induce structural distortion and eventual fatigue failure of key components on the screening machine if improperly designed. The proper design will require substantially heavier componentry to make it safe. The present invention requires only 1/6 to 1/3 of those weight requirements.
Drives disclosed in U.S. Pat. No. 4,472,980 issued to Wadensten and in U.S. Pat. No. 4,270,396 issued to Fallows both require complete, structurally integral housing entirely surrounding the drive to provide the necessary structural support to prevent undesired drive motion, vibrations, and main frame distortions. These bulky, heavy housings require the use of larger weights (2000 lbs total) in these inventions than those of the present invention (preferably approximately 700 lbs total) to produce the desired amount of force necessary to move the housing and unit as a whole. Thus, these references also require larger, more expensive motors to power the larger weights. The larger housings also necessitate that the drives take up a larger interior area of the particle screening machine than the present invention. Specifically, the height of the average particle screening machine having 200 square feet of screens per deck must be increased from the industry standard of about 3 feet to between 5 and 6 feet to allow placement of the bulky housing between the particle screens. The heavy drive housing, larger drive heights and drive motor, and deeper particle screening machine required by the prior art produce a particle screening machine and drive weighing between 20,000 and 30,000 pounds as opposed to the approximately 10,000 pound total weight drive and particle screening machine of the present invention. Importantly, the prior art drives, due to the above mass and height requirements of their housings, cannot function in a particle screening machine having a height of approximately 3 feet and 200 square feet of screen per deck. The prior art drives, to operate in a particle screening machine having 200 square feet of screen per deck, would require a drive shaft and associated weights about 18 inches in height, external housing covers located 6 to 10 inches above and below the weights, a drive coupling 6 to 8 inches long attaching the shaft to a motor, and a motor 12 to 24 inches in height. Thus, the overall height of the drive of the prior art is between 42 inches and 70 inches, as opposed to the approximately 12 inch to 16 inch height of the present invention. The above factors make the Wadensten and Fallows drives impractical for horizontal screening machines.
The above noted deficiencies of prior equipment are overcome in the present invention by a drive for a low profile particle screening machine of approximateldy 3 feet in height constructed to operate reliably at speeds above 250 RPM and pass particles freely in a practical, compact and convenient to operate and repair configuration.